metrologist

Today, two centuries later, the struggle for precision continues as metrologists devise ever more exacting techniques to measure quantities either so teeny or so gigantic that they had once been judged unmeasurable.

Cosmologist and metrologist Dr. John Hartnett points out that Ross is even wrong about the secular astronomy (personal communication).

Since the metrologists know the structure of the crystal, the volume occupied by an atom can be known.